The present invention relates to a coupling device adapted to connect a first rotatable part to a second part to be driven to a rotational movement, particularly a coupling device suitable to temporarly connect a workpiece to a machining apparatus in an angularly and centrically well defined relationship.
Upon fixing a workpiece on a machining apparatus (e.g. a turning lathe, a milling machine, a grinding machine or the like) it is of paramount importance that the workpiece to be treated in such a machine be connected thereto in a very precise manner with reference to the rotational axis of the machine. In the case of a turning lathe this is the rotational axis of the chuck, whereby the angular position of the workpiece relative to said axis is of no further importance. However the centricity of the workpiece relative to said axis must be observed with a high degree of precision. In the case of a milling or grinding apparatus not only the centricity is important, but also the angular position of the workpiece with reference to the axis of rotation of the machining apparatus must be observed.
During the construction of precision tools extremely high requirements must be observed with reference to the machining of a workpiece. Particularly it must be ensured that a workpiece to be machined is connected to a machining apparatus in an exactly defined position.
It is well known to use conically shaped receiving members to connect a workpiece to a machining apparatus, whereby tight tolerances may be achieved in view of eccentricity. However this conically shaped receiving members are subjected to contamination by environal influences and by chips which are generated during the operation of the machining apparatus. A contaminated conically shaped receiving member either is degraded in its precision or cannot be loosened any longer due to occuring of self-locking. In addition it is not possible to connect a workpiece by means of such conically shaped receiving members in an exactly defined angular position.
The same facts are true regarding the known and widely used chucks. They are also subjected to contamination during the machining process and do not offer any solution for receiving a workpiece in an angularly well defined position.
If a workpiece has to be machined to an extremely high degree of precision, the connecting members receiving the workpiece and fixing it to the machining apparatus must be manufactured with at least the same high degree of precision. This is true for conically shaped receiving members as well as for chucks, e.g. of a turning lathe. Of course such high precision involves well qualified workmanship and very high costs, which is especially disadvantageous if a relatively high number of such fixing members is required.
A still further problem not sufficiently solved until now may be seen in the fact that a workpiece may have to be fixed to a plurality of different machining apparatuses in order to perform a plurality of machining steps on the same workpiece. Thereby it is ensured that the workpiece always must be connected to the corresponding machining apparatus in an angularly and centrically well defined position with very high precision. For example, in forming an electrode tool of an electroerosive machining apparatus a plurality of machining operations is required which have to be performed on different machining apparatuses. The machining of these workpieces must be performed within a tolerance of plus or minus one thousandth of a millimeter whereby it would be most desireable to displace the workpieces from one machining station to the following one quickly and to fix the workpieces in an angularly and centrically well defined manner with very high precision.